1. Field of the Invention
The present invention relates to an antenna structure. The invention also relates to an expansion card. Furthermore, the invention relates to a method in the manufacture of an antenna structure.
2. Description of the Related Art
According to prior art, various electronic devices, such as portable personal computers (PC), are often equipped with an expansion card connection, to which a standard expansion card can be connected. The expansion card can contain the radio parts of a wireless communication device, including an antenna, wherein the PC can communicate with a communication network by means of this card-like wireless communication device. The expansion card may also constitute a network adapter e.g. for a wireless local area network (WLAN), wherein the card comprises the necessary electrical circuits e.g. for signal processing and for the transceiver. Said antennas are used for transmitting and receiving radio-frequency signals, and the signals are transferred between the radio part and the antenna by means of conductors and connectors.
Patent publication U.S. Pat. No. 5,966,097 presents a double antenna comprising an active antenna conductor which is a linear inverted-F antenna (IFA), and a parasitic straight antenna conductor. Each antenna conductor consists of conductors which are arranged in parallel on a ground plane and coupled at one end to this ground plane. The active antenna conductor is further coupled to a radio frequency (RF) feed point at a certain point. The wire-like antenna elements can be fixed and supported to the printed circuit board (PCB) used as the ground plane in different ways, of which examples are presented in patent publications U.S. Pat. No. 4,646,101 and U.S. Pat. No. 4,584,585. The plate-like elements can also be implemented with pieces cut and bent from a conductive metal sheet, fixed onto the PCB board where the ground plane is formed for example with a large conductive coating. One fixing method is also presented in patent publication U.S. Pat. No. 5,550,554.
In the assembly, the different antenna conductors of the double antenna are separately placed onto the circuit board, wherein the elements must be separated from each other at least for sorting. Furthermore, it must be possible to place the antenna conductor in the right direction onto the circuit board. Moreover, it should be possible to place the antenna conductors in a correct position to direct that end of the conductor which is connected to the ground plane in the desired direction. When the double antenna is used in a diversity antenna, at least two pieces of each antenna conductor will be required. In the diversity antenna, identical antennas are often used as mirror images of each other, wherein the possible positions of each conductor vary.
One problem is often the fact that antenna conductors of similar type differ from each other in the way of fixing them onto the circuit board. Thus, a diversity antenna consisting of two double antennas comprises a total of four different antenna conductors, whose positioning at the right place and handling must be taken care of. Patent publication U.S. Pat. No. 5,966,097 presents one prior art alternative, in which the antenna conductors are placed in the same support element. The positioning of also this support element must be taken care of as presented above, particularly in a diversity antenna, but the antenna conductors are readily in the correct position in relation to each other.
If the antenna elements are installed separately, changes and errors in the placement cause variations in the dimensions of the antenna structure which also have a harmful effect on the electrical operation.
It is an aim of the invention to eliminate the above-mentioned drawbacks related to the complication of the assembly and fixing of the antenna conductors, the slowness of the assembly steps, and the large number of various antenna elements. The invention relates to a double antenna whose electrical operation corresponds to the solution in patent publication U.S. Pat. No. 5,966,097, as well as to an optimized diversity antenna consisting of two said double antennas.
The main principle of the invention is the symmetry of the antenna structure and the conductors in view of the assembly, wherein the different position alternatives are reduced or totally eliminated and the assembly becomes easier and faster. One essential idea is also to place the symmetrical conductors of the double antenna in a common support frame which is further fixed onto the circuit board of a wireless communication device, an expansion card. The total manufacturing time of the expansion card can be reduced, since the antenna conductors do not need to be installed separately, and the way of installation resembles the way of assembling also the other components to be fixed onto the surface of the circuit board. Integration of the conductors related to the antenna in the same support frame provides advantages particularly in antennas, such as diversity antennas, which comprise several antennas or antenna conductors to be installed in different positions.
If the support element is for example a multi-layer or double-sided circuit board, the antenna can be manufactured by methods known as such by means of the circuit board material used as a dielectric, and strip conductors. A particular advantage is achieved in that variations in the dimensions caused by assembly of the antenna elements can be reduced by measuring accuracy of the circuit boards, wherein the operation of the antenna is more reliable.
Furthermore, an essential principle of the invention is to place the diversity antenna card in an optimized way in a housing for the expansion. Spurious signals emitted by processors and electrical circuits in electronic devices interfere with the operation of the antenna. When placed in a part used as an extension of the expansion card, the antenna structure can be taken out of the connection and further from the device.